Fuel injection valves fitted to internal combustion engines having two intake ports per cylinder, are generally constructed so that fuel can be injected into the two intake ports simultaneously. Such a fuel injection valve as disclosed in Japanese Utility Model Unexamined Publication No. 3-10066, has air paths formed on opposite sides of the fuel spray such that air discharged from the air paths (referred to hereunder as auxiliary air) is impacted onto the fuel spray.
This device, as well as promoting atomization and subsequent vaporization of the fuel spray by impacting the auxiliary air onto the fuel spray, also enables flattening of the cross-sectional shape of the fuel spray to suit the layout of the intake port (herein cross-sectional shape refers to the cross-sectional shape in a plane perpendicular to a central axis of the fuel spray). The device thus enables an improvement in combustion such as at low engine temperatures, and in particular a reduction in hydrocarbon emissions and an improvement in fuel consumption.
More specifically, the conventionally constructed fuel injection valve is mounted on an outer wall of a bifurcated intake port in the vicinity of the branch point thereof, so as to spray two fuel sprays from the fuel injection holes towards the respective two intake ports. The ends of each of the intake ports are however curved significantly towards the vertical direction of the cylinder. Consequently, the cross-sectional shape of the fuel spray is necessarily flattened so that the spray angle in a direction aligned with the two intake ports is greater than the spray angle in the direction perpendicular thereto.
To achieve this, auxiliary air is taken from upstream of the throttle valve and discharged from air ports on both sides of the fuel spray. The resultant impact of the auxiliary air promotes atomization and subsequent vaporization of the fuel spray while flattening the cross-sectional shape of the fuel spray shape, and thus also prevents fuel from adhering to the inner wall of the intake port.
The construction of the conventional fuel injection valve however has no provision for controlling the fuel spray after impact with the discharged auxiliary air, so that the flattened cross-sectional shape is highly susceptible to excessive spreading.
That is to say, the construction of the conventional fuel injection valve enables the promotion of atomization and subsequent vaporization of the fuel spray. However since the cross-sectional shape of the fuel spray can spread excessively due to the impact of the auxiliary air with the fuel spray, it becomes difficult to obtain an optimum fuel spray cross-sectional shape for the intake port layout. Consequently, the fuel spray impacts and adheres to the inner wall of the intake port, thus impeding the beneficial atomization and subsequent vaporization of the fuel spray resulting from impact with the auxiliary air.
Although the discharge amount, discharge velocity, and discharge position etc. of the auxiliary air may be optimized to control any excessive spreading of the cross-sectional shape of the fuel spray under conditions of constant fuel injection, the flattened spread cannot be controlled when there is an increase in fuel injection amount corresponding to a change in load. A good cross-sectional shape over the whole operating range is thus difficult to obtain.
In cases where it is not so necessary to flatten the cross-sectional shape of the fuel spray, such as when a good degree of flattening is obtained from the impact of fuel sprays discharging from a plurality of fuel injection holes, then when auxiliary air is impacted against the fuel spray to promote atomization of the fuel spray, the impact flattens the cross-section of the fuel spray more than necessary. There is thus again the problem of controlling the excessive flatness so as to form a desirable cross sectional shape.
Furthermore, in order to improve combustion, there is also the requirement to even further promote atomization and subsequent vaporization of the fuel spray.
Such problems as mentioned above are not confined to internal combustion engines having two intake ports per cylinder, but also exist with internal combustion engines having one (unbifurcated)intake port per cylinder.
In view of the above heretofore encountered problems, it is an object of the present invention to provide a fuel injection valve which can promote atomization and subsequent vaporization of a fuel spray by impacting a discharge of auxiliary air onto the fuel spray, and which can obtain an optimum fuel spray for various intake port layouts by controlling the cross-sectional shape and injection direction of the fuel spray.